稀土硼化物LaB_6晶体材料的弹性性质和力学性能
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摘要
利用密度泛函理论和Birch-Murnaghan物态方程,系统分析了LaB6晶体材料的弹性常数参数、体弹性模量、剪切弹性模量及其他力学性能。结果表明:LaB6晶体具有较大的弹性常数参数C11,说明在此主轴应力方向上具有较大的弹性常数;同时它还具有较大的体弹性模量,并且体弹性模量具有各向同性,剪切弹性模量具有各向异性;LaB6晶体的杨氏模量为227.85 GPa,泊松比为0.26,体剪弹性模量比值达到1.44,表明其脆性较强,不易发生弹性形变;LaB6晶体的硬度达到11.56 GPa,平均弹性波速达4.87 km/s。LaB6的带隙宽度为0.20 eV,呈金属性,内部电子具有较强的局域性,La和B之间具有较强的共价键成分。
The elastic constants parameters, bulk modulus, shear modulus and mechanical properties of the LaB_6 crystalline material have been systematically studied with density functional theory and the BirchMurnaghan formation. The results show that the LaB_6 has larger C11, indicating its larger elastic constant along this direction. The LaB_6 also has large bulk modulus, and the bulk modulus is isotropic, whereas the shear modulus is moderately anisotropic. The LaB_6 crystalline material has large Young's modulus of 227.85 GPa,so it is hard for elastic deformation. The Poisson's ratio is 0.26 and the B/G value is 1.44, these values indicate the moderate brittleness of this material. The hardness of LaB_6 is 11.56 GPa and the mean elastic velocity is 4.87 km/s. The LaB_6 has narrow band gap of 0.20 eV, showing that it is metallic type material.The electrons of LaB_6 have strong localization interaction, and there is covalent bond between La and B.
The elastic constants parameters, bulk modulus, shear modulus and mechanical properties of the LaB_6 crystalline material have been systematically studied with density functional theory and the BirchMurnaghan formation. The results show that the LaB_6 has larger C11, indicating its larger elastic constant along this direction. The LaB_6 also has large bulk modulus, and the bulk modulus is isotropic, whereas the shear modulus is moderately anisotropic. The LaB_6 crystalline material has large Young's modulus of 227.85 GPa,so it is hard for elastic deformation. The Poisson's ratio is 0.26 and the B/G value is 1.44, these values indicate the moderate brittleness of this material. The hardness of LaB_6 is 11.56 GPa and the mean elastic velocity is 4.87 km/s. The LaB_6 has narrow band gap of 0.20 eV, showing that it is metallic type material.The electrons of LaB_6 have strong localization interaction, and there is covalent bond between La and B.
引文
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[3]CHEN C H,AIZAWA T,IYI N,et al.Structural refinement and thermal expansion of hexaborides[J].Journal of Alloys and Compounds,2004,366(1/2):L6-L8.
[4]张宁,张玖兴,包黎红.悬浮区域熔炼法制备REB6(La B6、Ce B6)单晶体及其表征[J].功能材料,2012,43(2):178-180.ZHANG N,ZHANG J X,BAO L H,et al.Floating zone growth and characterization of single crystal REB3(La B6,Ce B6)cathode[J].Chinese Journal of Functional Materials,2012,43(2):178-180.
[5]包黎红,那仁格日乐,特古斯,等.放电等离子烧结原位合成Lax Ce1-x B6化合物及性能研究[J].物理学报,2013,62:196105.BAO L H,NARENGERILE,TEGUS O,et al.Synthesis and properties of Lax Ce1-x B6 compounds by in-situ spark plasma sintering[J].Acta Physica Sinica,2013,62:196105.
[6]刘洪亮,张忻,王杨,等.单晶La B6阴极材料典型晶面的电子结构和发射性能研究[J].物理学报,2018,67:048101.LIU H L,ZHANG X,WANG Y,et al.Surface electronic structures and emission property of single crystal La B6 typical surfaces[J].Acta Physica Sinica,2018,67:048101.
[7]高瑞兰,于化顺,于普涟,等.La B6多晶材料的制备工艺研究[J].山东大学学报(工学版),2002,32(6):593-596.GAO R L,YU H S,YU P L,et al.Preparation of La B6 polycrystalline materials[J].Journal of Shandong University(Engineering Science),2002,32(6):593-596.
[8]NYE J F.Physical properties of crystals:their representation by tensors and matrices[M].Oxford:Oxford University Press,1957.
[9]HILL R.The elastic behaviour of a crystalline aggregate[J].Proceedings of the Physical Society Section A,1952,65(5):349.
[10]TIAN Y,XU B,ZHAO Z.Microscopic theory of hardness and design of novel superhard crystals[J].International Journal of Refractory Metals and Hard Materials,2012,33:93-106.
[11]BORN M,HUANG K.Dynamical theory of crystal lattices[M].Oxford:Clarendon Press,1968.
[12]HAINES J,LEGER J M,BOCQUILLON G.Synthesis and design of superhard materials[J].Annual Review of Materials Research,2001,31(1):1-23.
[13]PANDA K B,CHANDRAN K S R.Determination of elastic constants of titanium diboride(Ti B2)from first principles using FLAPW implementation of the density functional theory[J].Computational Materials Science,2006,35(2):134-150.
[14]ANDERSON O L.A simplified method for calculating the Debye temperature from elastic constants[J].Journal of Physics and Chemistry of Solids,1963,24(7):909-917.